Mixtures Of N-heptane Research Articles

Modeling and experimental data of LLE, VLE, kinematic Viscosity, and density for the 2-Phenylethanol + n-Heptane mixture at low pressure

Modeling and experimental data of LLE, VLE, kinematic Viscosity, and density for the 2-Phenylethanol + n-Heptane mixture at low pressure

An improved manifold-projection trajectory based method for chemical kinetic mechanism reduction

An improved manifold-projection trajectory based dimension reduction algorithm (MTDR) to automatically generate skeletal chemical kinetic mechanisms was proposed and validated in this study. This algorithm is implemented by constructing an approximate manifold-based trajectory of the combustion system using Euclidean distances between two adjacent points and cosine similarities between two adjacent vectors in the manifold space, and then evaluating the importance of species by calculating the error of manifold-based trajectories before and after the projection of the manifold. In this method, the nature of the combustion system is well reflected since the combustion process information can be captured by the location of the state point in the manifold space. The calculation during the reduction process is simplified by using the manifold-based trajectory instead of the complex differential equations. Compared to our previous work, this study improves the prediction accuracy of the reduced mechanisms through a more comprehensive error evaluation in the mechanism reduction process. The detailed mechanisms of fuels including iso-cetane, iso-octane and gasoline surrogate mixtures of toluene, iso-octane and n-heptane were reduced to portray the prowess of the algorithm. It’s demonstrated that the number of species of the fuels is reduced from 492, 254 and 1389 to 95, 87 and 427 within an acceptable error, respectively. Meanwhile, the case of iso-octane mechanism reduction was chosen to compare the performance of MTDR with traditional methods including path flux analysis (PFA) and directed relation graph with error propagation and sensitivity analysis (DRGEPSA), and it is shown that the MDTR can generate more compact mechanism under a broad range of error limits.

Exploring the Effect of Relaxation Time, Natural Surfactant, and Potential Determining Ions (Ca2+, Mg2+, and SO42−) on the Dynamic Interfacial Tension Behavior of Model Oil-Brine Systems

This study examined how the concentration of asphaltene and divalent ions in various salinities affects the interfacial tension (IFT) between a model oil/brine using the pendant drop method. The oleic phase consisted of a mixture of toluene and n-heptane (heptol), to which asphaltene was added to investigate how asphaltene molecules affect the surface properties. The base fluid was prepared with a salinity of 40,000 ppm, and two additional solutions with concentrations of 4000 ppm (low salinity) and 80,000 ppm (high salinity) were created. The results revealed that increasing the concentration of asphaltene within certain salinity ranges led to a decrease in IFT. The lowest IFT was observed at the 40,000 ppm salinity level, indicating that at this optimal salinity, the maximum asphaltene concentration migrated to the heptol/brine interface, reducing the IFT from 23 mN/m to 16 mN/m. Additionally, a 0.5 % wt of asphaltene demonstrated a significant concentration of micellization of natural surfactants, suggesting that the interface was nearly saturated with asphaltene. Consequently, concentrations higher than this value did not significantly alter the IFT. In the final part of the study, the impact of divalent ions was investigated, revealing that as the concentration of Ca2+ ions increased up to fourfold, the IFT decreased to 15 mN/m, about 10 % less than the base case. This value represented the lowest IFT compared to Mg2+ and SO42−. Moreover, modeling the results indicated that the relaxation time decreased with increasing salinity, suggesting that higher salinity accelerated the process of asphaltene absorption at the interface.

Solubility measurement and correlation for γ-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane in four binary solvents (ethyl acetate + n-hexane, n-heptane, n-octane, iso-octane) at temperatures from 283.15 K to 323.15 K

The solubility of γ-CL-20 in four binary solvents (n-hexane, n-heptane, n-octane, iso-octane mixtures of n-hexane, n-heptane, n-octane and iso-octane mixed with various mole fractions of ethyl acetate) was determined using the gravimetric method at temperatures ranging from 283.15 K to 323.15 K under atmospheric pressure in this work. The experimental solubility data of γ-CL-20 were correlated and fitted to the thermodynamic models such as the modified Apelblat equation, van’t Hoff equation, CNIBS/R-K equation, and Jouyban-Acree model. In the temperature range of 283.15 K–323.15 K. The solubility of γ-CL-20 declines monotonically and slowly with increasing temperature and the temperature dependence is invisible in all of the solution systems. Additionally, it demonstrates that the solubility in binary solvent combinations rises as the ethyl acetate (EtOAc) mole fraction does.

Simplification of the combustion mechanism of Jatropha biodiesel surrogate fuel and reaction path analysis

The objectives of this study were to explore the evolution process of the chemical reaction pathways in the combustion of a biodiesel surrogate fuel and to reduce the calculation burden in the numerical simulation of this combustion process due to the complicated mechanism. A mixture of methyl decanoate, methyl 9-decanoate, and n-heptane was selected as the Jatropha biodiesel surrogate fuel. A simplified combustion mechanism of the biodiesel comprising 170 components and 737 reaction components was formed by systematically simplifying 3299 components and 10806 reaction mechanisms using a multistep directed relation graph method, path flux analysis, and sensitivity analysis. The simplified mechanism was compared with the detailed mechanism and experimental data to effectively verify the accuracy of the mechanism. The simplified mechanism could reproduce the detailed mechanism, and the results were in good agreement with the experimental data in terms of the ignition time of a methyl decanoate/air mixture in a shock tube, the concentrations of the components generated in the combustion process of the biodiesel in a jet stirred reactor, and the flame propagation speed of methyl decanoate and n-heptane/air mixture. The rate of production analysis method was used to explore the main reaction pathways and the evolution process of important intermediate components in the Jatropha biodiesel surrogate fuel generated at high and low temperatures. Methyl decanoate and methyl 9-decanoate formed hydrogen peroxide ketone and oxy groups mainly through dehydrogenation, oxygenation, and isomerization at low temperatures. The high-temperature stage mainly involved bond-breaking decomposition reactions, partial dehydrogenation, and isomerization reactions of low-temperature reaction products, resulting in the formation of small molecular products.

Autoignition of two-phase n-heptane/air mixtures behind an oblique shock: Insights into spray oblique detonation initiation

Autoignition of n-heptane droplet/vapor/air mixtures behind an oblique shock wave are studied, through Eulerian-Lagrangian method and a skeletal chemical mechanism. The effects of gas/liquid equivalence ratio (ER), droplet diameter, flight altitude, and Mach number on the ignition transient and chemical timescales are investigated. The results show that the ratio of chemical excitation time to ignition delay time can be used to predict the oblique detonation wave (ODW) transition mode. When the ratio is relatively high, the combustion heat release is slow and smooth transition is more likely to occur. In heterogeneous ignition, there are direct interactions between the evaporating droplets and the induction/ignition process, and the chemical explosive propensity changes accordingly. The energy absorption of evaporating droplets significantly retards the ignition of n-heptane vapor. In the two-phase n-heptane mixture autoignition process, the ignition delay time decreases exponentially with flight Mach number and increases first and then decreases with the flight altitude. As the liquid ER increases, both ignition delay time and droplet evaporation time increase. With increased droplet diameter, the ignition delay time decreases, and the evaporation time increases. Besides, when Mach number is less than 10, the ratio of the chemical excitation time to ignition delay time generally increases with the flight altitude or Mach number. It increases when the liquid ER decreases or droplet diameter increases. When the Mach number is sufficiently high, it shows limited change with fuel and inflow conditions. The ODW is more likely to be initiated with a smooth transition at high altitude or Mach number. Abrupt transition mode tends to happen when fine fuel droplets are loaded. The results from this work can provide insights into spray ODW initiation.

Inhibition of asphaltene deposition by Al2O3 nanoparticles during CO2 injection

Carbon dioxide flooding is of interest due to its high oil-sweep efficiency for enhanced oil recovery and contribution to the reduction of greenhouse gas emissions. However, when CO2 is injected into deep geological strata, asphaltene may precipitate. In this work, the effect of Al2O3 nanoparticles on the deposition of asphaltene was examined by assessing the variations of bond number and interfacial tension at different pressures and a temperature of 60 °C. The asphaltene onset point and intensity were characterized using the bond number, which proved a better indicator of changes in oil droplet shape and interfacial tension with gravity. Synthesized mixtures of toluene and n-heptane that contained two different kinds of asphaltenes were used as M and D oil samples. A 0.06 mass% addition of Al2O3 nanoparticles, which worked best for reduction of interfacial tension, was also applied at various pressures. Addition of nanoparticles to the oils prevented asphaltene precipitation in both synthetic samples by altering the slope of the plot of interfacial tension with pressure by 49.7% for the M sample and 9.0% for the D sample. The Al2O3 nanoparticles were found to be more effective at inhibiting asphaltene precipitation for the M oil sample due to its lower H/C ratio and higher nitrogen content.

An environmentally benign, energy intensified single-column side stream extractive distillation (SC-SSED) process for Acetone/n-heptane separation

The single-column, side-stream extractive distillation (SSED) process has been proposed as a simple, novel, and energy-saving configuration for separating azeotropic mixtures, using an intermediate-boiling entrainer. However, within limited progress in separating the mixture of acetone (ACE) and n-heptane (HEP) through such processes, benzene (BEN), a human carcinogen, was frequently used as an entrainer. In view of this, our study aims to propose an environmentally benign SSED process to separate the same mixture. In the proposed process, 1-chlorobutane (CHL) is used as an entrainer. With thorough analysis, the economic performance of this process was found to outperform the other process using heavy entrainers (i.e. p-xylene and butyl propionate), while being economically comparable to the process using BEN as an entrainer. In addition, limited improvement is achieved by employing the SSED configuration for heavy entrainer-based processes, since a higher-grade steam is required at the reboiler of the extractive distillation column. Subsequently, a suitable control strategy with two temperature loops and three measurements (i.e. a side-stream temperature control loop, and a temperature difference control loop in the extractive section of the SSED column) was established. It can satisfactorily reject the specified feed disturbances (i.e. ±20% change in flowrate and composition). Compared to all other existing studies, the currently proposed control structure does not require any composition loop and, at the same time, is able to handle disturbances to a greater extent.

The contribution of intermediate-temperature heat release to octane sensitivity

Carbon footprint reduction can be achieved by increasing the efficiency of combustion engines. For spark-ignition (SI) internal combustion engines (ICE), fuel octane sensitivity (OS)—defined as the difference between a fuel’s research octane number (RON) and motor octane number (MON)—can help identify ideal fuels for avoiding unwanted knocking conditions. Moreover, it will help to extend the range of operating conditions that can be used in next-generation high-efficiency engines. Presently, there is a controversy over whether high or low OS fuels are beneficial for increased efficiency of next-generation engines depending on application and technology, e.g. high OS fuels are advantageous for down-sized and turbocharged spark-ignition (SI) engines, whereas low OS fuels are superior in novel systems such as pre-chamber engines. This work aims to improve the understanding of the impact of OS on the combustion performance of engines by analyzing the contribution of intermediate-temperature heat release (ITHR) to OS. The heat release of several mixtures of toluene, iso-octane, and n-heptane with similar RON but varying OS were studied under homogeneous charge compression ignition (HCCI) conditions in a cooperative fuel research (CFR) engine. This method gives insight into the heat release of the auto-igniting fuel without the obfuscation of the spark-ignited flame. At RON conditions, ITHR was a marker of OS. Furthermore, a new parameter called ITHR sensitivity was defined as the difference between the ITHR measured at RON conditions and the ITHR measured at MON conditions. ITHR sensitivity decreased with increasing octane sensitivity. This shows that non-sensitive fuels experience a greater change in the amount of ITHR as compared to sensitive fuels when changing from MON conditions to RON conditions. Thus, for engines requiring high OS fuels, it is recommended that components with high ITHR sensitivity are used and vice-versa for engines requiring low OS fuels.

Measurement and Simulation of Autoignition-Assisted Flame Speed of N-Heptane Mixture at Elevated Gas Temperature

Laminar flame speed and autoignition are two fundamental characteristics of a hydrocarbon’s combustion. These two characteristics are extensively studied due to their importance in designing and developing combustion systems. However, a regime in which these two characteristics simultaneously affect the combustion process is not well understood. Thus, the primary focus of this investigation is to understand the autoignition-assisted flame regime prior to the first-stage heat release. The premixed mixture of n-heptane in oxygen–nitrogen–diluent at an equivalence ratio of 1.0, a compressed gas pressure of 6.85 bar, and compressed gas temperatures of 621 K (when using argon) and 616 K (when using helium) were studied in this work. At these initial conditions, the mixture ignition delays are 32.31 ms (using argon) and 53.92 ms (using helium). The flame-propagating images were recorded using a high-speed camera at different spark ignition times to measure the flame locations. The Rapid Compression Machine─Flame (RCM-Flame) apparatus was used to perform experiments, and one-dimensional modeling and three-dimensional numerical modeling were performed. The simulations provided data to understand the effect of stretch on the measured spherical burning velocity. The measured and simulated autoignition-assisted laminar flame speeds were in excellent agreement, the linear method can be used to remove the stretch from the spherical burning velocity, and the autoignition-assisted flame speeds show a negligible dependency on the spark ignition times when the first-stage heat release is negligible.

Analysis of the interfacial tension of cationic imidazolium-based ionic liquid, twin-branched tailed anionic surfactant, and a non-ionic emulsifier in the presence of SiO2 nanoparticle and amphiphilic oleic components using response surface method

Although various surface active agents have been proposed, there is still no straightforward and clear understanding of the effect of cationic imidazolium-based ionic liquid (IL), twin-branched tailed anionic surfactant, and a non-ionic emulsifier in the presence of SiO2 nanoparticle and amphiphilic oleic components on the interfacial tension (IFT) reduction. So, in this work, the performance of cationic imidazolium-based IL ([C12mim][Cl], anionic surfactant (AOT)), and non-ionic surfactant (Tween 80) on the IFT value were studied through the design of experiment approach and the response surface method. Experiments were designed using a face-centered composite design (FCCD) with the independent variables of surfactant concentration (175–525 ppm) and nanoparticle concentration (25–75 ppm) as numerical ones, and surfactant type and synthetic oil (8 wt% of asphaltene and resin fractions dissolved in heptol (mixture of n-heptane: toluene with the volume ratio of 30:70)) with various volume ratios of asphaltene to resin (1:0, 2:1, 1:1, and 1:2) as categorical ones. According to the analysis of variance (ANOVA) and 156 measured IFT experimental data points, the effects of each factor were evaluated. As a result, the suggested quadratic model with R2 (0.9986) and adjusted R2 (0.9984) values indicated that the fitted model can accurately predict the response variable (IFT) values. The best performance (lower IFT and critical micelle concentration) was obtained for [C12mim][Cl] without being affected by the amphiphilic nature of asphaltene and resin fractions and the concentration of SiO2 nanoparticles. The appropriate surface activity of IL was attributed to the effective polar head group of imidazolium and the presence of nitrogen in the aromatic ring.

Critical, supercritical and phase-transition properties of binary 1-propanol + n-heptane mixtures

PρTx relationship of four binary 1-propanol + n-heptane mixtures was measured using high-temperature and high-pressure constant-volume piezometer technique in the critical, supercritical, and in the immediate vicinity of the liquid–gas phase transition curve. The experimental temperature and pressure ranges were from (373 to 623) K and up to 60 MPa. The liquid–gas critical loci behavior in the (Tc-x), (Pc-x), (ρc-x), and (Pc-Tc) projections, were studied based on the measured PρTx data. The values of the Krichevskii parameter for the (1-propanol + n-heptane) mixture were calculated using the measured critical curves data. Pure- and mixture-like behavior of the weakly (Cvx) and strongly (KTx and CPx) divergent properties has been studied based on measured critical curve data. The measured mixture molar volumes and pure components data were used to calculate the excess molar volumes. The values of the second virial coefficient of the mixture were calculated based on the measured PVTx data.

Calculating the Enthalpy of Vaporization of Ethanol, n-Heptane, Isooctane, and a Binary Mixture of Isooctane + n-Heptane from Their Vapor Pressure Data

ConspectusA key physical property of volatile liquids is vapor pressure (VP). Volatile organic compounds (VOCs) are a classification of compounds directly associated with low boiling points, high rates of evaporation, and high flammability. The majority of chemists and chemical engineers were directly exposed to the odor of simple ethers, acetone, and toluene in the air while taking an organic chemistry laboratory course as an undergraduate student. These are just a few examples of the numerous VOCs produced by the chemical industry. When toluene is poured into a beaker from its reagent bottle, its vapors readily evaporate at ambient temperature from this open container. When the cap is securely placed back on the reagent bottle of toluene, a dynamic equilibrium develops and exists in this closed environment. This chemical concept is known as a vapor-liquid phase equilibrium. A crucial physical property of spark-ignition (SI) fuels is high volatility. In the United States, most of the vehicles traveling on the road today have SI engines. Gasoline is the fuel used to power these engines. It is a major product manufactured by the petroleum industry. This fuel is petroleum based since it is a refined product of crude oil consisting of a mixture of hydrocarbons, additives, and blending agents. Thus, gasoline is homogeneous solution of VOCs.The VP as a function of temperature of a pure VOC can readily be measured using an ebulliometer. The VP is also known in the literature as the "bubble point pressure". In this investigation, the VP as a function of temperature was acquired for the VOCs ethanol, isooctane (2,2,4-trimethylpentane), and n-heptane. The latter two VOCs are primary reference fuels components found in 87, 89, and 92 grade gasoline. Ethanol is an oxygenate additive of gasoline. The VP of a homogeneous binary mixture of isooctane and n-heptane was also acquired using the same ebulliometer and methodology. In our work, an enhanced ebulliometer was used to collect the VP data in our work. It is known as the vapor pressure acquisition system. The devices that comprise the system automatically acquire the VP data and log it into an excel spreadsheet. The data are readily transformed into information to compute the heat of vaporization (ΔHvap). The results described in this Account compare quite favorably to the literature values. This validates our system for performing fast and reliable VP measurements.

Impact of Methanol and Butanol on Soot Formation in Gasoline Surrogate Pyrolysis: A Shock-Tube Study.

The influence of methanol and butanol on soot formation during the pyrolysis of a toluene primary reference fuel mixture with a research octane number (RON) of 91 (TPRF91) was investigated by conducting shock-tube experiments. The TPRF91 mixture contained 17 mol % n-heptane, 29 mol % iso-octane, and 54 mol % toluene. To assess the contribution of individual fuel compounds on soot formation during TPRF91 pyrolysis, the pyrolysis of argon diluted (1) toluene, (2) iso-octane, and (3) n-heptane mixtures were also studied. To enable the interpretation of the TPRF91 + methanol and TPRF91 + butanol experiments, the influence of both alcohols on soot formation during the thermal decomposition of toluene and iso-octane was also investigated in a separate series of measurements. Pyrolysis was monitored behind reflected shock waves at pressures between 2.1 and 4.2 bar and in the temperature range of 2060-2815 K. Laser extinction at 633 nm was used to determine the soot yield as a function of reaction time. For selected experiments, the temporal variation in temperature was also measured via time-resolved two-color CO absorption using two quantum-cascade lasers at 4.73 and 4.56 μm. It was found that soot formed during TPRF91 pyrolysis is primarily caused by the thermal decomposition of toluene. Adding methanol to TPRF91 results in a slight reduction of soot formation, whereas admixing butanol results in shifting soot formation to higher temperatures, but in that case, no overall soot reduction was observed during TPRF91 pyrolysis. Measured soot yields were compared to simulations based on a previous and an updated version of a detailed reaction mechanism from the CRECK modeling group [Nobili, A.; Cuoci, A.; Pejpichestakul, W.; Pelucchi, M.; Cavallotti, C.; Faravelli, T. Combust. Flame 2022; 10.1016/j.combustflame.2022.112073]. Rate-of-production analyses for reactions involving BINS at different experimental conditions were carried out. Although in the case of TPRF91 and toluene pyrolysis, no quantitative agreement was obtained between the experiment and simulation, the comparison nevertheless shows that the new version of the CRECK mechanism is a significant improvement over the previous one. In the case of n-heptane decomposition and iso-octane pyrolysis with and without alcohols, the updated reaction mechanism shows excellent agreement between simulation and measured soot yields.

Effect of entrainers with different boiling point sequences on the design and performance for side-stream extractive distillation processes

BackgroundAn azeotropic mixture of acetone and n-heptane is commonly found in many pharmaceutical wastewaters. In this work, the separation of acetone / n-heptane was studied using intermediate- and high-boiling-point entrainers (benzene and p-xylene, respectively). MethodsTo maximize the economic benefits and mitigate the economic and environmental impact of the separation process, traditional extractive distillation and side-stream extractive distillation processes were developed for different entrainers. The sequential iteration method was employed to optimize the extractive distillation process, with the total annual cost as the constraint objective. Significant findingsThe results show that p-xylene can facilitate the separation of acetone / n-heptane, with high efficiency and low energy consumption, when using a double distillation column. Among the four separation processes developed, the p-xylene side-stream extractive distillation process delivers the best economic and environmental performance, with a total annual cost of 6.04 × 105 $/y and CO2 emissions of 1114.66 kg/y. Compared to the case of traditional p-xylene extractive distillation and benzene side-stream extractive distillation processes, the total annual cost of the p-xylene side-stream extractive distillation process was reduced by 9.56% and 49.22%, respectively, while the corresponding CO2 emissions were reduced by 15.71% and 48.85%.

An Experimental and Computational Study on Triple Injection Strategies to Reduce Cold Start Diesel Engine Emissions

Abstract The effect of triple injection strategies in a diesel engine to reduce cold start emissions were experimentally and computationally investigated in this work. The experiments were performed using a 1.9 L four-cylinder, turbocharged compression ignition engine with diesel fuel. As a representative of the cold start condition in the diesel engine, a low load condition of 1500 rpm and 2 bar brake mean effective pressure (BMEP) was chosen as the fixed condition for this study. The injection strategy made use of a late post injection to reduce catalyst light-off time. The pilot and main injections are fixed and the post injection timing is swept later into the expansion stroke to increase exhaust enthalpy available to heat the aftertreatment system. To further understand the source of hydrocarbon (HC) emissions from late injections, equivalent experiments were conducted with a mixture of n-heptane and iso-octane that matched the reactivity of the diesel fuel. The mixture of primary reference fuels (i.e., PRF 34) obtained by matching the cetane number (CN) of diesel fuel, showed similar combustion characteristics of diesel, but is much more volatile due to lighter components in the PRF mixture. The increased volatility of PRF 34 suppressed liquid fuel impingement on the cylinder liner, which isolated liner impingement as a possible source of HC emissions. Simulations were also performed for the present engine configuration and operating conditions in a sector mesh using CONVERGE™. The physical properties of diesel fuel were modeled using a five-component surrogate. The chemical kinetics of the diesel fuel were modeled with a reduced n-heptane model. The simulations were able to capture the experimental trends of combustion characteristics and emissions. The HC emissions were observed to increase for both fuels with retarded post injection timings in engine experiments. PRF 34 had comparable HC emissions to diesel experiments, which indicated that the liner impingement is not the main source of the increase in HC emissions. Overmixing of the fuel and air was identified as the major cause of increase in HC emissions. Additionally, exhaust gas recirculation (EGR) also intensified the overmixing phenomenon and thereby increase in HC emissions.

ESIPT in a binary mixture of non-polar and protic polar solvents: Role of solvation dynamics

Excited-state intramolecular proton transfer (ESIPT) was studied for two different fluorophores M2N3HF and 2P3HBQ in binary solvent mixtures of n-heptane and methanol. While both fluorophores share a degree of structural resemblance, they exhibit sharply contrasting ESIPT dynamics in the solvent mixtures. For 2P3HBQ, ESIPT is ultra-fast in n-heptane, followed by monotonic retardation in the solvent mixtures as the proportion of methanol increases, due to the predominance of 2P3HBQ⋯Methanol intermolecular H-bonding over intramolecular H-bonding within the 2P3HBQ molecule, at high methanol concentrations. For M2N3HF on the other hand, ESIPT is known to occur within sub-picosecond time-scales in alkanes and within few tens of picoseconds in methanol. However, addition of minor quantities of methanol into an alkane solvent like n-heptane causes the ESIPT to be dramatically arrested: even at 3 % mole fraction of methanol, it requires several 100 ps to complete, thus becoming ∼ 1000-fold slower than that in pure n-heptane, and ∼ 5-fold slower than that in pure methanol. Our results demonstrate that the ESIPT time-constants of M2N3HF in the solvent mixtures follow the same trend as solvation time-constants, suggesting that solvent relaxation plays a major role in the re-distribution of intra- and intermolecular H-bonds in the excited state M2N3HF. Unlike 2P3HBQ, the ESIPT of M2N3HF is thus coupled to the solvation dynamics of the solvent medium.

Investigation of Aggregation Behavior and Molecular Weight Changes of Asphaltene Model Compound

We investigate the aggregation of Violanthrone-78 (VO-78), a model asphaltene compound, in mixtures of toluene and n-heptane (heptol) using spectroscopic and dynamic and static light scattering techniques. The light scattering experiments were conducted using pure toluene and n-heptane, as well as 25/75, 50/50, and 75/25 heptol solvents. Furthermore, the concentration of VO-78 varied from 10-8 M to 10-3 M in these suspensions. The dynamic light scattering experiments were used to study the aggregate sizes from the intensity autocorrelation function at different n-heptane volume fractions. The results show the onset of aggregation of about 50 % n-heptane volume fractions. The aggregate sizes in toluene, within the range of concentrations examined, were below the instrument's detection limit (< 5 nm) but increased with increasing dosages of n-heptane. On the other hand, the aggregate size in pure heptane was observed to be greater than the maximum limit of the instrument (> 10 μm). Furthermore, the static light scattering experiments provided an anomalous behavior. Increasing concentrations of VO-78 in the solvent resulted in lowering the parameter Kc/Rq, where c is the molar concentration.

Catalytic enantioselective 5-endo-bromocycloetherification of unactivated cyclic alkenes

This study reports the development and scope of catalytic enantioselective 5-endo-trig bromocycloetherification of six-membered unactivated alkenes having a hydroxyethyl group. The proposed reaction occurs in a chiral anionic phase-transfer catalytic system using a combination of a binaphthol-based chiral phosphoric acid and a derivative of DABCO bromine complex to provide bicyclic tetrahydrofuran-fused 6-membered products, which bear a bromo group at the bridgehead position with complete diastereoselectivity and good to high enantioselectivity. Results show that the enantioselectivity depends on the solvent system and substituents at the 3,3′-position of the catalyst. Thus, the best result can be obtained using a catalyst that has 2,4,6-tricyclohexylphenyl groups at the 3,3′-positions in a mixture of fluorobenzene and n-heptane. In addition, the construction of a quaternary carbon center with the retention of configuration via a radical mediated allylation of the tertiary bromo group in the product was reported.

Soot formation in n-heptane/air laminar diffusion flames: Effect of toluene addition

The mixture of n-heptane and toluene is regarded as surrogate fuel for diesel. Under the premise of a certain carbon flow rate, the particle size, nanostructure, microcrystalline size and soot deposition morphology of three kinds of fuel laminar diffusion flames were studied by Transmission Electron Microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM), X-ray diffractometer (XRD) and Field Emission Scanning Electron Microscopy (FESEM). The three fuels were pure n-heptane (T0), toluene / n-heptane blends with 5 vol% (T5) and 10 vol% (T10) toluene, respectively. Thermophoretic probe sampling and SiC fiber deposition were used to obtain soot samples. The results showed that with the increase of toluene content, the flame height increased and the temperature decreased at the same height. The addition of toluene increased the content of PAHs, which promoted the formation of soot, and increased the number and particle size of soot. At HAB = 30 mm, with the increase of toluene content, the graphitization degree of soot increased, which showed a larger soot fringe length and a smaller fringe tortuosity, and microcrystalline width (La) of soot particles increased gradually. It is worth noting that the size of a new structure in the soot deposition is counted for the first time, and it is found that its size is negatively correlated with the fringe length and microcrystalline width of soot.